In frequency division multiplexed (PDM) Continuous Phase Modulation (CPM) multiple access systems, the spectral efficiency can be increased by reducing the spacing between adjacent channels, thus allowing some overlap in frequency and hence admitting a certain amount of interference. When a multiuser receiver is adopted, the benefits in terms of spectral efficiency can be very large (the signals can be packed denser and denser see refs [2], [4]).
Unfortunately, the complexity of the optimal multi-user detector varies exponentially with the number of users, and specifically for the case of CPM the implementation on to state-of-the art digital hardware platforms is not realistic (the required amount of computations per second translates to extremely high power consumption and very costly design even for tens of users).